Vol. 7, No. 8, August 1968
NOTES 1675 become nearly close-packed whereas the coordination numbers of the atoms remain unchanged.
700 -
Acknowledgment.-The 65-kbar experiments were supervised by C. L. Hoover, the X-ray data were obtained by K. R. Babcock, M. S.Licis, and J. F. Whitney, and the dta experiments were performed by H. W. Williams.
G
CONTRIBUTION FROM THE
w
I
DEPARTMENT OF CHEMISTRY, LAKECITY, UTAH 84112
UNIVERSITY O F UTAH, SALT
73 J
B
Complexes of Titanium Tetrafluoride with Substituted Pyridines B Y JOHN
Received March 22, 1968
Co Zn Fe 500 72
74
76
78
00
w. DOWNING AND RONALD 0 . RAGSDALE
02
VOLUME FOR AO,
84
06
80
i3
Figure 1.-Plot of the volumes of AM004 molybdates vs. the volumes of corresponding A 0 oxides with the rock salt structure.
and the a-MnMoOl structure is the coordination of Mo which is tetrahedral in a-MnMoO4 and essentially octahedral in a-CoMoOr. Tetrahedral Mo also occurs in AMo04 molybdates where A is Ca, Sr, Ba, Cd, or Pb (scheelite structure). The occurrence of tetrahedral or octahedral Mo in AM004 molybdates would thus appear to depend on the’ size and electronegativity of the A cation. The two most electropositive cations in the series, Mg, Mn, Zn, Fe, Co, and Ni are Mg and Mn, and of this series it is only Mg and Mn that form normal (STP) molybdates with tetrahedral molybdenum. While Mn is the largest of the above series, h1g is not the second largest. I n Figure 1 the cell volumes of the Ani1004 molybdates are plotted against the cell volumes of the rock salt A 0 compounds.12 The trends are relatively consistent although magnesium appears to be larger in the molybdates than in MgO. The figure dramatically shows the large density difference between the a-CoMoo4 isotypes and the NiW04 isotypes. This is interesting because in both of these structure types the A and Mo atoms are in octahedral coordination. However, the oxygen atoms are nearly closed-packed in the NiWOi structure type whereas this is not the case in the a-CoMo04 structure. Smith arid Ibers:’ describe the oxygen packing in a-CoMoO4 as cubic-close-packed except that one out of nine oxygen sites is vacant. Thus, during the transformation from the a-CoMoOl structure to the NiWOJ structure the oxygeii atoms ( l a ) D a t a for the rock salt cell volumes were taken Et-om R.W. G. Wyckoff, “Crystal Structures,” Vol. I , 2nd ed, John Wiley and Sons, Inc., New York. N. Y., 1963, pp 86-91, except the value for ZnO which was obtained from C. H . Bates, W. B. White, and R. Roy, Science, 157,993 (1962).
Most of the titanium tetrafluoride complexes described in the literature have been with monofunctional oxygen donors. Usually the complexes are cis adducts of the type TiF4.2 (donor), thus reflecting the tendency of titanium to achieve sixfold coordination. I n contrast to the large number of oxygen-containing diadducts, very few complexes have been reported with other donor atoms. Reactions of various amines with TiF4 have been in~estigated.‘-~Reactions with secondary amines have resulted in aminolysis reactions with the formation of dialkylamidotitanium(1V) trifluorides and dialkylammonium hexafluorotitanates. 1 , 2 With tertiary amines and pyridine, addition compounds are formed.2 Depending upon reaction conditions, it is possible to obtain both the 1:1 complex and 2: 1 camplex, TiF?.2py, with (py = pyridine). The 2: 1 complex slowly loses pyridine on standing in a dry atmosphere. The addition compound appeared to be polymeric and the titanium was postulated to be octahedrally coordinated through fluorine bridging.4 No FI9nmr data were reported for the pyridine complexes. As a result, we felt i t of interest to prepare complexes of several substituted pyridines in an attempt to clarify their structure(s) by nuclear magnetic resonance spectroscopy. Experimental Section Materials.-Dimethoxyethane obtained from Matheson Coleman and Bell was dried by distillation from sodium metal. Titanium tetrafluoride obtained from Allied Chemical Co. was used without further purification. 2-Chloropyridine, 2-bromopyriditie, 3-broriiopyridiiic, atid 3-cliloropyridine obtained from Aldricli Cheiiiical Co ., pyridine, 2-iiiethylpyridiiie (Practical grade), 4-methylpyridine, and 2,tLdirnethylpyridine (Practical grade) obtained from Eastman Organic Chemicals, and 2,4dimethylpyridine (Practical grade) obtained from Matheson Coleman and Bell were dried by distillation from calcium oxide. (1) J. A . Chandler, J. E. Wuller, a n d K. S. Ihago, h w g . Chani., 1, 0 5 (1962). (2) J. A. Chandler and R . S . Drago, ibid., 1, 356 (1962). (3) H. J . Emelbusand G. S. Rao, J . Chem. Soc., 4245 (1958). (4) E. L.Muetterties, J . Am. Chetn. SOL.,82, 1082 (1960).
1676 NOTES
Inorgunic Chemistry
Elemental analyses were performed by Alfred Bernhardt Mikroanalytisches Laboratorium, Miilheim, West Germany. Preparations of Complexes.-The substituted pyridine was added slowly to a saturated solution of TiF4 in dimethoxyethane until precipitation ceased. The solid was collected by filtration and dried under vacuum. Anal. Calcd for TiF4.4-CH3CsH4N: C, 33.21; H , 3.25; N, 6.45. Found: C, 33.07; H, 3.77; N, 6.62. Calcd for TiF4.2,6-(CH~)2CjH3N:C, 36.39; H, 3.92; N, 6.06. Found: C, 37.72; H , 4.97; S,6.68. Calcd for TiF4. 3-BrCjH4N: C, 21.30; H, 1.42; N, 4.96; Br, 28.35. Found: C, 22.72; H , 1.84; N, 5.14; Br, 30.54. Instrumental Data.-The fluorine nmr spectra were obtained on a Varian A56/6OA spectrometer equipped with a V-6057 variable-temperature accessory. The chemical shifts were measured with respect to external standard trichlorofluoromethane.
complexes have high melting points which are not sharp. The intractability of the compounds and the absence of sharp melting points suggest that the 1: 1 adducts are not pentavalent complexes. In all probability they are polymeric complexes with “fluorine bridging” so that the titanium is octahedrally coordinated. This phenomenon has been observed in antimony p e n t a f l ~ o r i d e , ~arsenic ~’~ fluorosulfonate,l 1 and other fluorides.12 h similar conclusion was reached by Muetterties4 for the TiF4 py complex. To explain their conductometric titration curve for the titration of TiF4 by pyridine in acetone, Chandler and Drago2 proposed the mechanism
Results Complexes of TiF4 with 4-methyl-, 2-methyl-, 2,Gdimethyl-, 3-chloro-, 2-chloro-, 3-bromo-, and 2bromopyridines were prepared. Of these, only the 2-chloro- and 2-bromopyridine complexes were soluble upon addition of base to the TiF4-dimethoxyethane solution ; the other complexes precipitated immediately and were insoluble in a wide variety of solvents. Thus, i t was possible to obtain the F19nmr spectra of only the 2-halopyridine complexes. These spectra, obtained in dimethoxyethane at -Bo,consisted of two triplets of equal intensity. The data from these spectra are given below. The chemical shifts are uncorrected for
+ py +[TiFd.py] [ T i R . p y ] + 2TiF4 --+pyTiFs+ + Ti2Fs2py + pyTiFa+ + T i 8 (X/x)(pyTiFd),
Ligand
2-Chloropyridine 2-Bromopyridine
Chem shifts, ppm (external C F C h ref)
F-F coupling constants, cps
-146, -214 -146, -214
34 36
bulk susceptibility.
Discussion The spectra of the 2-chloropyridine and 2-bromopyridine complexes are consistent with the previously reported cis-TiFd 2(donor) The F19 spectra consist of two 1: 2 : 1 triplets of equal intensity, indicating that the two donor molecules must be cis to each other. The chemical shifts5 and coupling constants8 are similar to those for other cis-TiF, diadducts. Elemental analyses of the insoluble complexes (4methylpyridine, 2,6-dimethylpyridine, and 3-bromopyridine) show them to be essentially 1:1 complexes. No evidence was found for the formation of 2 : l adducts with any of the substituted pyridines which formed 1: 1 complexes. The 1: 1 complexes have very little solubility in polar, nonprotonic solvents. A large range of solvents was employed, but it was not possible to dissolve enough of the compounds (for >0.02 M solutions) to obtain their spectra. The compounds are soluble with decomposition in protonic solvents such as water and ethanol. The 2-methylpyridine adduct was shown to be a 1: 1 complex by decomposing the complex in water, obtaining the H’ nmr spectrum, integrating the methyl resonance, and comparing it with data for standard 2-inethylpyridine-water solutions. ‘I’hcse
-
( 5 ) 11. 0. Ragsdale and B. B. Stewart, Iizorg. C h e w . , 2 , 1002 (1903). (6) U. S.Dyer and R. 0. Ragsdale, Chem. Commun., 601 (1966). ( 7 ) D. S. Dyer and R. 0. Ragsdale, I n o u g . Chem., 6, 8 (1967). ( 8 ) D. S . Dyer and R. 0. Rasgdale, J . Phys. C h e m . , 71,2309 (1967).
TiF4
---f
I n this reaction scheme one should consider that the titanium species achieve sixfold coordination complexing with the solvent. By also including additional reaction [TiFe,py]
+ py
TiF4.2py
(2’)
the formation of the cis diadducts can be explained. There is competition between reactions 2 and 2’ and one would expect an increase in basicity of the ligand to favor reaction 2 thus influencing the extent of polymer formation, i.e., insolubility. The stronger the base the more readily a fluoride ion could be transferred from T i F 4 . p ~to a TiF, molecule. I n Table I are listed pK, values of pyridine and some substituted pyridines. As can be seen from these data, the diadducts were formed with the two weakest bases. TABLE I THE PYRIDINES AND THEIR TITAXIUM TETRAFLUORIDE
RELATIVE BASICITY OF COMPLEXES WITH Ligand
pKRa
Solubility
Stoichiometry
1.31 Sol 2: 1 1.60 Sol 2: 1 2.20 Insol 1:l 2.16 Insol 1:lb 5.14 Insol 1:lc 6.12 Insol 1:l 4-Methylp yridine 6.15 Insol 1:l 2,fi-Dimethylpyridine 6.73 Insol 1:l 2,4-Dimethylpyridine 6.74 Insol 1: I d I. I. Grandberg, G. I(. Faizova, and A. N. Kost, K h i m Geterotsikl. Soedin, 4, 561 (1966). Stoichiometry established by similarity of its physical propcrtics with thc othcr 1: 1 comReference 4. plexcs. References 2-4. 2-Chloropyridine 2-Brotnopyridiiie 3-Bromopyridine 3-Chloropyridine Pyridine 2-Methylpyridine
It is interesting that a 2: 1 adduct n-as not obtained with 3-bromopyridine where there is not a large difference in its basicity as compared to 2-bromopyridine. The pK, values give the relative basicity of the pyridines toward hydrogen ion, but with respect to the larger reference acid, TiF4,the basicity of the 2-bromo(9) C. A. Hoffman, B. E. Holder, and W. L. Jolly, i b i d . , 62, 364 (39583. (10) l
